1. Field of the Invention
The present invention relates to using hydrocarbon waste materials, more specifically, heavy petroleum hydrocarbons including petroleum sludge, tank bottoms, or residue having an API gravity of about five to about thirty into useful fuels and products.
2. Background of the Invention
Oil producers generate significant amounts of petroleum waste materials. For example, operating companies generate a significant volume of petroleum waste materials, including thousands of cubic meters of oily wastes annually, much of which are tank bottoms sludge and various refinery and production wastes. Furthermore, various amounts of non-leaded hydrocarbon products, waste solvents, and slop oil waste materials are generated. These waste materials are often contaminated by water and insoluble solids. Some of these sludges contain between fifty to ninety percent oil. The annual disposal costs for these materials can be a significant operating expense to operating companies, which is lost. Much of these materials are now “land-farmed” creating potential environmental problems. In the USA and elsewhere, such disposal techniques are believed to have led to highly toxic superfund sites. Furthermore, local regulations are expected to limit or eliminate land farming in the near future. Therefore, it is important that proper steps are taken to utilize or dispose of such waste materials.
Heavy residue, petroleum waste, and sludge materials are formed during production, handling, and processing of the petroleum hydrocarbons. The transportation and use of the heavy hydrocarbons are difficult because of their high viscosity and poor stability. At ambient conditions, heavy hydrocarbons, such as a refinery residue, have an API gravity of about thirty or less. These oily materials are often contaminated with solid or semi-solid waste materials and water.
Due to improvements in the refining processes over the past fifty years, additional lighter products are being recovered from every barrel of hydrocarbon waste oil. Thus, the residue and heavy materials, such as bunker fuel, being produced in various refineries are undergoing significant changes in quality including a greater concentration of asphaltenes. The presence of a larger concentration of asphaltenes in fuels has a great impact on fuel usage in various applications. Asphaltenes are polar compounds that tend to agglomerate into very large structures in liquid hydrocarbons. These agglomerates lead to viscosities that are much higher than if the asphaltenes were not structured. The asphaltene molecule appears to carry a core of approximately five stacked flat sheets of condensed aromatic rings, one above the other giving an overall height of sixteen to eighteen Angstroms. The average sheet diameter appears to range from six to fourteen Angstroms. The molecular weight of petroleum asphaltenes can range from about 1,000 to 50,000. A refinery residue after it is extracted with a solvent exists in a solid state such that its viscosity cannot be measured, and one has to heat the material at a sufficiently high temperature (>100° C.) to make this material into a low viscosity material suitable for transport.
In storage tanks or tankers, fuel sludge, tank bottom, etc. are formed when asphaltenes are separated from the fuel and deposited on the bottom of the tank. Furthermore, fuel sludges are formed when different fuels including residual fuels are blended when one of the components contains significant amount of asphaltene. In hydrocarbon waste upgraded by hydrotreating and hydrocracking processes, the relatively unreactive portion of the hydrocarbon waste, termed “residue,” can be formed, which requires further processing. Refinery wastes, tank bottoms sludge, waste solvents, slop oil, lube oil waste, and other hydrocarbon waste produced during refining are environmentally hazardous and can create a disposal problem. In blending of different hydrocarbon wastes or hydrocarbon waste products, asphaltene/resin ratio is altered and fuels become unstable as asphaltenes separate and agglomerate. Furthermore, as stated earlier, fuel sludges are formed when different fuels including residual fuels are blended, especially when one of the components contains higher amounts of asphaltenes. During transportation, asphaltenes deposit and clog reservoir pores and pipelines. Utilization of hydrocarbon waste involves various steps such as storage, transportation, and combustion, partial oxidation or further refining and the like. The presence of asphaltenes can affect each of these steps.
U.S. Pat. No. 5,133,781 issued to DeRosa et al. discloses a method of stabilizing asphaltenes in hydrocarbons by dissolving the asphaltenes in tetrahydrofuran, phosphochlorinating the asphaltenes, and then reacting the phosphochlorinated-asphaltenes with equimolar amounts of aliphatic or aromatic alcohols. The '781 patent stabilizes the asphaltenes for use in bituminous liquids until well into the refining process.
Attempts have been made to convert sewage sludge waste into useful fuels. As an example, in U.S. Pat. No. 5,356,540 issued to Khan, a pumpable aqueous slurry of sewage sludge is produced by the step of dewatering the sewage sludge to produce an aqueous slurry having a solids content of about 10 to 25 wt. %. The aqueous slurry of sewage sludge is then pretreated to improve its slurrying characteristics by one or a combination of (a) heating, (b) hydrothermal treatment, and (c) heating, mixing and shearing the aqueous slurry of sewage sludge. The following materials are then mixed together at a temperature in the range of about ambient to 400° F. to produce a pumpable aqueous slurry having a solids content in the range of about 30 to 65 wt. %: (a) pretreated aqueous slurry of sewage sludge; (b) a nonionic water-soluble alkoxylated alkylphenol additive; and (c) sewage sludge-containing material and/or solid carbonaceous fuel-containing material to increase the solids loading. When using the techniques taught by this patent with industrial hydrocarbon sludge streams, the effects are often limited in duration.
Introduction into refining, partial oxidation (gasification), or combustion processes are possible avenues to dispose of petroleum hydrocarbons, such as tank bottoms sludge or residue. Having 5% by weight or greater asphaltene concentration in asphaltene-rich hydrocarbons, however, tends to cause difficulties in pumping, fuel injections, atomization, spray and combustion or partial oxidation. Asphaltene rich particles have a long burning time, which results in larger flame size. Combustion ignition is delayed for these fuels. In a combustion chamber, unburned carbon and soot are produced. Other difficulties include excessive wear in piston ring and cylinder liner; fracture of piston rings, and increased deposits on combustion chamber. During combustion, the presence of asphaltenes creates non-homogeneous fuel mixtures that result in a non-uniform spray pattern. Larger fuel particles containing asphaltenes do not atomize or vaporize contributing to incomplete combustion that leads to deposits and various pollutants being formed in the combustion system.
A need exists for a method of utilizing petroleum hydrocarbon wastes that will reduce disposal costs and risks associated with disposal of the hydrocarbon wastes. A goal is to provide a process that utilizes the hydrocarbon waste as a fuel source in a process that will not result in deleterious results within the process. A further goal is to provide a process that efficiently utilizes the asphaltenes contained within hydrocarbon waste streams.